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COVID-19 severity among patients with multiple sclerosis treated with cladribine: A systematic review and meta-analysis

Published:September 02, 2022DOI:https://doi.org/10.1016/j.msard.2022.104156

      Abstract

      Background

      The Coronavirus 19 pandemic has raised new relevant questions regarding the management of patients with multiple sclerosis (pwMS) treated with different immunosuppressive and immunomodulant drugs. In most COVID-19 outcomes analyses, due to the small available sample size, patients treated with cladribine were grouped with patients treated with other treatments.

      Methods

      Three major databases (PubMed, Scopus and Web of Science) and the most recent MS congress libraries were searched for extracting original articles on COVID-19 and multiple sclerosis. The key inclusion criteria were the presence of data on pwMS treated with cladribine and with documented positivity for COVID-19. The quality of the included studies was evaluated using a modified version of the Dutch Cochrane center critical review checklist proposed by MOOSE. A common-effect meta-analysis was used for estimating the pooled proportion of patients with severe events (hospitalizations, pneumonia, ICU admissions and deaths) and heterogeneity was assessed by the I2 statistic.

      Results

      13 articles were included in the analysis and the median quality of the articles reached a level of 4. The selected studies included 5138 patients with COVID-19, of whom 107 (2.1%) were treated with cladribine. Pooled estimates of hospitalization and death were 9.36% and 0% for patients treated with cladribine, 14.98% and 2.66% for pwMS under other treatments.

      Conclusion

      These results indicate that pwMS treated with cladribine are not at a greater risk of developing a severe form of COVID-19.

      Registration

      The protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO: CRD42022329464),

      Keywords

      1. Introduction

      The coronavirus disease 2019 (COVID-19), due to its significant and unpredictable long-lasting impact on public health, has raised relevant questions regarding the infection risk in vulnerable patients and the management of subjects treated with immunotherapies (
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      Risk of getting COVID-19 in people with multiple sclerosis: a case-control study.
      ). In fact, immunosuppressive conditions, whether it is induced by immunological disorders or by medications, may alter immunocompetence modifying the ability to mount an effective immune response to infection and/or vaccination (
      • Agrati C.
      • Di Cosimo S.
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      COVID-19 vaccination in fragile patients: current evidence and an harmonized transdisease trial.
      ).
      Multiple sclerosis (MS), a chronic demyelinating disorder of the central nervous system (CNS), involves immune response abnormalities and is often treated with disease modifying therapies (DMTs), causing different degrees of systemic immunosuppression. For these reasons, patients with MS (pwMS) might be exposed to an increased risk of COVID-19 severe complications (
      • Capasso N.
      • Palladino R.
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      Prevalence of SARS-CoV-2 antibodies in multiple sclerosis: the hidden part of the iceberg.
      ;
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      • Antel J.P.
      • Giacomini P.S.
      COVID-19 and disease-modifying therapies in patients with demyelinating diseases of the central nervous system: a systematic review.
      ) and so they are considered as fragile subjects. Taking into account the infection contagiousness and the hospital promiscuity during the first wave of COVID-19 pandemic, also the disease management, from therapeutic strategies to scheduling routine clinical follow-up and rehabilitation plans, has undergone to a considerable change (
      • Sharifian-Dorche M.
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      • Fadda G.
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      • Antel J.P.
      • Giacomini P.S.
      COVID-19 and disease-modifying therapies in patients with demyelinating diseases of the central nervous system: a systematic review.
      ).
      At the beginning of COVID-19 spread, different empirical recommendations were developed by scientific societies for assisting the neurologists in the management of pwMS and indicating either to delay or to continue treatments, depending on their mechanisms of action, the impact, and the effects duration on the immune-system (
      • Laroni A.
      • Schiavetti I.
      • Sormani M.P.
      • Uccelli A.
      COVID-19 in patients with multiple sclerosis undergoing disease-modifying treatments.
      ). These national and international guidelines were initially more precautionary, subsequently the first evidence became available allowing a better evaluation of the DMTs safety profile and an update of the different scientific societies’ positions.
      So far, different evidence has been published regarding the evaluation of the impact of DMTs on the severity of COVID-19 in pwMS. They are largely reassuring but they have also suggested that MS therapies may be related to a different severity of COVID-19 infection (
      • Laroni A.
      • Schiavetti I.
      • Sormani M.P.
      • Uccelli A.
      COVID-19 in patients with multiple sclerosis undergoing disease-modifying treatments.
      ;
      • Sormani M.P.
      • De Rossi N.
      • Schiavetti I.
      • Carmisciano L.
      • Cordioli C.
      • Moiola L.
      • Radaelli M.
      • Immovilli P.
      • Capobianco M.
      • Trojano M.
      • Zaratin P.
      • Tedeschi G.
      • Comi G.
      • Battaglia M.A.
      • Patti F.
      • Salvetti M.
      • Nozzolillo A.
      • Bellacosa A.
      • Mantero V.
      the Musc-19 Study Group
      Disease-modifying therapies and coronavirus disease 2019 severity in multiple sclerosis.
      ;
      • Salter A.
      • Fox R.J.
      • Newsome S.D.
      • Halper J.
      • Li D.K.B.
      • Kanellis P.
      • Costello K.
      • Bebo B.
      • Rammohan K.
      • Cutter G.R.
      • Cross A.H.
      Outcomes and risk factors associated with SARS-CoV-2 infection in a north american registry of patients with multiple sclerosis.
      ;
      • Simpson-Yap S.
      • De Brouwer E.
      • Kalincik T.
      • Rijke N.
      • Hillert J.A.
      • Walton C.
      • Edan G.
      • Moreau Y.
      • Spelman T.
      • Geys L.
      • Parciak T.
      • Gautrais C.
      • Lazovski N.
      • Pirmani A.
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      • Forsberg L.
      • Glaser A.
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      • Schmidt H.
      • Bergmann A.B.
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      • Butzkueven H.
      • Alroughani R.
      • Ozakbas S.
      • Rojas J.I.
      • van der Mei I.
      • Nag N.
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      • Brum D.
      • Mendes M.F.
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      • Bauer J.
      • Chertcoff A.S.
      • Zabalza A.
      • Arrambide G.
      • Fidao A.
      • Comi G.
      • Peeters L.
      Associations of disease-modifying therapies with COVID-19 severity in multiple sclerosis.
      ) and have consistently correlated risk factors as male sex, an older age, the presence of comorbidities, and higher disability to a more severe disease outcome (
      • Sormani M.P.
      • De Rossi N.
      • Schiavetti I.
      • Carmisciano L.
      • Cordioli C.
      • Moiola L.
      • Radaelli M.
      • Immovilli P.
      • Capobianco M.
      • Trojano M.
      • Zaratin P.
      • Tedeschi G.
      • Comi G.
      • Battaglia M.A.
      • Patti F.
      • Salvetti M.
      • Nozzolillo A.
      • Bellacosa A.
      • Mantero V.
      the Musc-19 Study Group
      Disease-modifying therapies and coronavirus disease 2019 severity in multiple sclerosis.
      ;
      • Salter A.
      • Fox R.J.
      • Newsome S.D.
      • Halper J.
      • Li D.K.B.
      • Kanellis P.
      • Costello K.
      • Bebo B.
      • Rammohan K.
      • Cutter G.R.
      • Cross A.H.
      Outcomes and risk factors associated with SARS-CoV-2 infection in a north american registry of patients with multiple sclerosis.
      ;
      • Louapre C.
      • Collongues N.
      • Stankoff B.
      • Giannesini C.
      • Papeix C.
      • Bensa C.
      • Deschamps R.
      • Créange A.
      • Wahab A.
      • Pelletier J.
      • Heinzlef O.
      • Labauge P.
      • Guilloton L.
      • Ahle G.
      • Goudot M.
      • Bigaut K.
      • Laplaud D.-A.
      • Vukusic S.
      • Lubetzki C.
      Clinical characteristics and outcomes in patients with coronavirus disease 2019 and multiple sclerosis.
      ).
      Cladribine tablets, counted among immune cell depleting medications, is a purine chlorinated analog of deoxyadenosine that acts through the transient depletion of lymphocytes followed by immune reconstitution phase. As a semi-selective therapy, its effects are more pronounced on the adaptive immune response, impacting most specific B subsets than T cells, while its impact on the innate immune system is limited (
      • Amor S.
      • Baker D.
      • Khoury S.J.
      • Schmierer K.
      • Giovanonni G.
      SARS-COV -2 and multiple sclerosis: not all immune depleting DMTS are equal or bad.
      ;
      • Zheng C.
      • Kar I.
      • Chen C.K.
      • Sau C.
      • Woodson S.
      • Serra A.
      • Abboud H.
      Multiple sclerosis disease-modifying therapy and the COVID-19 pandemic: implications on the risk of infection and future vaccination.
      ).
      In most COVID-19 outcomes analysis, due to the small available sample size, patients treated with cladribine were grouped with patients treated with other treatments, often in the “other DMT” group (
      • Sormani M.P.
      • De Rossi N.
      • Schiavetti I.
      • Carmisciano L.
      • Cordioli C.
      • Moiola L.
      • Radaelli M.
      • Immovilli P.
      • Capobianco M.
      • Trojano M.
      • Zaratin P.
      • Tedeschi G.
      • Comi G.
      • Battaglia M.A.
      • Patti F.
      • Salvetti M.
      • Nozzolillo A.
      • Bellacosa A.
      • Mantero V.
      the Musc-19 Study Group
      Disease-modifying therapies and coronavirus disease 2019 severity in multiple sclerosis.
      ;
      • Salter A.
      • Fox R.J.
      • Newsome S.D.
      • Halper J.
      • Li D.K.B.
      • Kanellis P.
      • Costello K.
      • Bebo B.
      • Rammohan K.
      • Cutter G.R.
      • Cross A.H.
      Outcomes and risk factors associated with SARS-CoV-2 infection in a north american registry of patients with multiple sclerosis.
      ;
      • Louapre C.
      • Collongues N.
      • Stankoff B.
      • Giannesini C.
      • Papeix C.
      • Bensa C.
      • Deschamps R.
      • Créange A.
      • Wahab A.
      • Pelletier J.
      • Heinzlef O.
      • Labauge P.
      • Guilloton L.
      • Ahle G.
      • Goudot M.
      • Bigaut K.
      • Laplaud D.-A.
      • Vukusic S.
      • Lubetzki C.
      Clinical characteristics and outcomes in patients with coronavirus disease 2019 and multiple sclerosis.
      ;
      • Dalla Costa G.
      • Leocani L.
      • Montalban X.
      • Guerrero A.I.
      • Sørensen P.S.
      • Magyari M.
      • Dobson R.J.B.
      • Cummins N.
      • Narayan V.A.
      • Hotopf M.
      • Comi G.
      Real-time assessment of COVID-19 prevalence among multiple sclerosis patients: a multicenter European study.
      ;
      • Mantero V.
      • Abate L.
      • Balgera R.
      • Basilico P.
      • Salmaggi A.
      • Cordano C.
      Assessing the susceptibility to acute respiratory illness COVID-19-related in a cohort of multiple sclerosis patients.
      ), and therefore it is not possible to derive results specifically related to patients treated with cladribine. .
      We conducted here a meta-analysis for estimating the severity of COVID-19 events, evaluated as mortality and hospitalization rate, among patients treated with cladribine. The methodology is the same used in another review referring to anti-CD20 drugs category (
      • Schiavetti I.
      • Ponzano M.
      • Signori A.
      • Bovis F.
      • Carmisciano L.
      • Sormani M.P.
      Severe outcomes of COVID-19 among patients with multiple sclerosis under anti-CD-20 therapies: a systematic review and meta-analysis.
      ).

      2. Methods

      2.1 Article selection

      A comprehensive online search of the literature to detect the most relevant studies published from 2020 to March 2022 was performed in Scopus, Web of Science, PubMed and among the abstracts presented at the 2020 and 2021 ECTRIMS meeting and the most relevant congresses held before March 2022.
      The search strategy consisted of a combination of terms and keywords as follows: for PubMed Database: (MS) OR (Multiple Sclerosis) AND (COVID-19 OR Coronavirus OR SARS-CoV-2 OR Covid) AND (cladribine); for Scopus Database: (TITLE-ABS-KEY (coronavirus OR covid OR COVID-19 OR sars-cov-2) AND TITLE-ABS-KEY (cladribine) AND TITLE-ABS-KEY (ms OR multiple AND sclerosis)); for Web of Science: MS or multiple sclerosis (All Fields) and cladribine (All Fields) and Covid or coronavirus or COVID-19 or SARS-CoV-2 (All Fields).
      The systematic review included articles reporting data on COVID-19 course for pwMS treated with cladribine. However, studies were excluded if they were out of topic, systematic reviews and duplicated manuscripts among the sources, with overlapping patients.
      Eligibility assessment of the first screening was performed independently by two reviewers (AA and IS), based on title and abstract. The second examination was done on full text with the inclusion and exclusion criteria reported above by both reviewers (AA and IS), independently. Disagreements between the reviewers were resolved by double-checking and discussion to achieve a consensus.
      The following data were extracted from the identified studies: authors, title, country, sample size, number of males/females, mean age with range, number of patients with progressive MS, number of patients with relapsing MS, median last EDSS, mean MS duration with range, most recent MS treatments, number of hospitalizations (overall and for pwMS treated with Cladribine), number of patients admitted to the ICU, number of patients with pneumonia, number of deaths (overall and for pwMS treated with Cladribine). In case of missing data, an email was sent to the corresponding authors asking to complete the lacking information.
      The review protocol was registered with PROSPERO (registration number: CRD42022329464).

      2.2 Quality assessment

      The quality of selected articles was evaluated by two authors according to a modified version of the Dutch Cochrane center critical review checklist proposed by MOOSE (
      • Stroup D.F.
      Meta-analysis of observational studies in epidemiologya proposal for reporting.
      ). The key MOOSE domains include: (I) Clear definition of study population; (II) Clear definition of outcomes and outcomes assessment; (III) Independent assessment of outcome parameters; (IV) Sufficient follow-up; (V) No selective loss during follow-up; and (VI) Important confounders and prognostic factors identified. Each domain, based on published data, could be completed, and rated as follows: yes (1 point), no/unclear (0 points). However, since two domains (IV and V) were considered irrelevant for the purpose of this analysis, only four (I, II, III, VI) were combined in an overall reporting quality score (ranging from 0 to 4 points). A study was defined of highest quality if all criteria were rated as “yes” because free from intra-study bias.

      2.3 Outcomes

      The outcomes selected for the evaluation of Covid-severity among all pwMS with confirmed positivity were: the number of hospitalization, the presence of pneumonia, the number of ICU admissions and cases of deaths. For the subgroup of patients in treatment with cladribine, only number of hospitalization and deaths were considered as clinical outcomes.

      2.4 Statistical analysis

      A pooled estimate of the proportion of hospitalizations, and deaths among pwMS was obtained by a common-effect meta-analysis with logit transformation. The I2 statistic (the ratio of between-study variance to the observed variance) was computed for quantifying heterogeneity.
      Case reports were excluded from the meta-analysis to avoid overestimating the rate of severe outcomes (case reports usually refer to severe cases). Meta-analysis was performed using R software, version 4.1.3 (packages “metafor” and “meta”).

      3. Results

      The first literature search revealed a total of 190 publications, 76 were excluded for potentially duplicated or overlapping data. Of the remaining 114, 7 were selected for the final analysis, along with 6 retrieved out from search strategy (Fig. 1). References of 13 selected manuscripts (
      • Sormani M.P.
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      • Moiola L.
      • Radaelli M.
      • Immovilli P.
      • Capobianco M.
      • Trojano M.
      • Zaratin P.
      • Tedeschi G.
      • Comi G.
      • Battaglia M.A.
      • Patti F.
      • Salvetti M.
      • Nozzolillo A.
      • Bellacosa A.
      • Mantero V.
      the Musc-19 Study Group
      Disease-modifying therapies and coronavirus disease 2019 severity in multiple sclerosis.
      ;
      • Salter A.
      • Fox R.J.
      • Newsome S.D.
      • Halper J.
      • Li D.K.B.
      • Kanellis P.
      • Costello K.
      • Bebo B.
      • Rammohan K.
      • Cutter G.R.
      • Cross A.H.
      Outcomes and risk factors associated with SARS-CoV-2 infection in a north american registry of patients with multiple sclerosis.
      ;
      • Louapre C.
      • Collongues N.
      • Stankoff B.
      • Giannesini C.
      • Papeix C.
      • Bensa C.
      • Deschamps R.
      • Créange A.
      • Wahab A.
      • Pelletier J.
      • Heinzlef O.
      • Labauge P.
      • Guilloton L.
      • Ahle G.
      • Goudot M.
      • Bigaut K.
      • Laplaud D.-A.
      • Vukusic S.
      • Lubetzki C.
      Clinical characteristics and outcomes in patients with coronavirus disease 2019 and multiple sclerosis.
      ;
      • Hervas-Garcia J.V.
      • Gil-Sanchez A.
      • Gonzalez-Mingot C.
      • Nogueras L.
      • Quibus L.
      • Sancho A.
      • Quirant B.
      • Peralta S.
      • Solana M.J.
      • Ramo C.
      Seroprevalence of SARS-CoV-2 in multiple sclerosis patients under immunomodulatory treatment in lleida (study em COVID-19).
      ;
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      Clinical course and outcome of SARS-CoV-2 infection in multiple sclerosis patients treated with disease-modifying therapies - the Polish experience.
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      SARS-CoV-2 infection in multiple sclerosis: results of the spanish neurology society registry.
      ;
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      Increased rate of hospitalisation for COVID-19 among rituximab-treated multiple sclerosis patients: a study of the Swedish multiple sclerosis registry.
      ;
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      Coronavirus disease 2019 in Latin American patients with multiple sclerosis.
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      COVID-19 severity and outcome in multiple sclerosis: results of a national, registry-based, matched cohort study.
      ;
      Clinical Outcomes
      Clinical outcomes in patients with COVID-19 during two phase IV studies of cladribine tablets for treatment of multiple sclerosis: an update (P11-4.005).
      ) are shown in Table 1.
      Table 1List of included studies.
      NrFirst authorTitleJournalYear
      01Louapre C.Clinical Characteristics and Outcomes in Patients with Coronavirus Disease 2019 and Multiple SclerosisJAMA Neurol.Jul,2020
      02

      Oreja-Guevara C.COVID-19 in cladribine-treated patients with Multiple Sclerosis8th Joint ACTRIMS-ECTRIMS MeetingSep,2020
      03Hervás-García J. V.Seroprevalence of SARS-CoV-2 in multiple sclerosis patients under immunomodulatory treatment in lleida (study emCOVID-19)Mult Scler.Dec,2020
      04Salter A.Outcomes and Risk Factors Associated With SARS-CoV-2 Infection in a North American Registry of Patients with Multiple SclerosisJAMA Neurol.Mar,2021
      05Czarnowska A.Clinical course and outcome of SARS-CoV-2 infection in multiple sclerosis patients treated with disease-modifying therapies - the Polish experienceNeurol Neurochir Pol.Apr,2021
      06Sormani M. P.Disease-Modifying Therapies and Coronavirus Disease 2019 Severity in Multiple SclerosisAnnals of NeurologyJan,2021
      07Arrambide G.SARS-CoV-2 Infection in Multiple Sclerosis: Results of the Spanish Neurology Society RegistryNeurol Neuroimmunol Neuroinflamm.Jun,2021
      08

      Spelman T.Increased rate of hospitalization for COVID-19 among rituximab-treated multiple sclerosis patients: A study of the Swedish multiple sclerosis registryMult Scler.Jul,2021
      09Drulovic J.Humoral response to SARS-CoV-2 COVID-19 vaccines in patients with multiple sclerosis treated with immune reconstitution therapiesMult Scler Relat Disord.Jul,2021
      10Fragoso Y. DCoronavirus disease 2019 in Latin American patients with multiple sclerosisMult Scler Relat Disord.Jul,2021
      11Bsteh G.COVID-19 severity and mortality in multiple sclerosis are not associated with immunotherapy: Insights from a nation-wide Austrian registryPlos oneJul,2021
      12Perez A. C.COVID-19 severity and outcome in multiple sclerosis: Results of a national, registry-based, matched cohort studyMult Scler Relat Disord.Aug,2021
      13Yavorskaya V.Clinical Outcomes in Patients With COVID-19 During Two Phase IV Studies of Cladribine Tablets for Treatment of Multiple Sclerosis:

      An Update
      AAN 2022Apr,2022
      The median quality score of included studies was 3.0 (range 1–4) but considering implemented details provided by authors the value improved to 4.0 (range: 2–4) (Fig. 2).
      These 13 selected studies include 5138 adult pwMS with COVID-19 infections, aged between 17 and 82 years, females for the 72%, with a disease duration ranging from 0 to 40 years and with relapsing remitting form of the disease for about 82%. Out of 5138 pwMS, 107 patients (2.1%) were in treatment with cladribine. The baseline characteristics are reported in Table 2.
      Table 2Baseline characteristics.
      NrFirst AuthorDemographyMS dataDisease Modifying Treatments
      SampleFemales/MalesAge, yrs (range)Progressive/RRLast EDSSMS duration, yrs(range)DMT unknownUntreatedCladribineAlemtuzumabAzathioprineGlatiramer AcetateDimethyl fumarateFingolimodInterferon betaMethotrexateMitoxantroneNatalizumabOcrelizumabRituximabTeriflunomideOzanimodOther
      01Louapre C.347249/9831.8-57.465/2822.03.5-23.56331033354220105738173304
      02Oreja-Guevara C.149/528.1-52.11/131.00.8-18.6001400000000000000
      03Hervás-García J. V.1912/741-671/182.03-2400110052300232000
      04Salter A.16261202/42134.5-60.9280/12753.2-232371498420810653201704847782141
      05Czarnowska A.396282/11418-6824/3722.00-33051042164168203352002530
      06Sormani M. P.844593/25118-82135/6762.04.7-17.115111141070174947311858956402
      07Arrambide G.326221/10533.3-56.363/2632.03-195961801341273600262333377
      08Spelman T.476340/13619–7867/4072.00.0–40.7188594820185772621113
      09Drulovic J.1813/533-51.10/183.06.6-22.2011(+7)
      Out of 18 patients in treatment with Cladribine, 11 developed COVID-19 infection. In some manuscripts DMTs and/or MS type are not available for all individuals
      00000000000000
      10Fragoso Y. D.7350/2317-724/692.00-26031101015141000653500
      11Bsteh G.12690/3621-7928/982.08372211119166001012200
      12Perez A. C.843616/22739.8-70.65115111554514261872172417
      13Yavorskaya V.3025/519-55003000000000000000
      low asterisk Out of 18 patients in treatment with Cladribine, 11 developed COVID-19 infection. In some manuscripts DMTs and/or MS type are not available for all individuals
      Findings from COVID-19 severity outcomes and results from the meta-analysis are reported in Table 3. A total of 1029 out of the 5138 included patients were hospitalized (pooled estimate: 14.98%; 95%CI = [10.47%; 20.97%]), and 157 died (pooled estimate: 2.66%; 95%CI = [1.79%; 3.92%]). Among the 107 patients treated with cladribine and reporting COVID-19 severity outcomes, 7 were hospitalized (pooled estimate: 9.36%; 95%CI = [4.73%; 17.69%]) (Fig. 3A) and no deaths were reported (pooled estimate: 0.00%; 95%CI = [0.00%; 1.17%]) (Fig. 3B).
      Table 3COVID-19 severity outcomes.
      OVERALLCLADRIBINE
      NrAuthorNHospitalizationPneumoniaICU admissionDeathNHospitalizationDeath
      01Louapre C.34773 (21.0%)-4 (1.2%)12 (3.5%)32 (66.7%)0 (0.0%)
      02Oreja-Guevara C.141 (7.1%)1 (7.1%)0 (0.0%)0 (0.0%)141 (7.1%)0 (0.0%)
      03Hervás-García J. V.191 (5.3%)1 (5.3%)0 (0.0%)0 (0.0%)1
      Case reports excluded from the meta-analysis
      0 (0.0%)0 (0.0%)
      04Salter A.1626320 (19.7%)112 (6.9%)104 (6.4%)54 (3.3%)141 (7.1%)0 (0.0%)
      05Czarnowska A.39627 (6.8%)1 (0.3%)-1 (0.3%)50 (0.0%)0 (0.0%)
      06Sormani M. P.84496 (11.4%)99 (11.7%)38 (4.5%)13 (1.5%)110 (0.0%)0 (0.0%)
      07Arrambide G.32669 (21.2%)-7 (2.1%)7 (2.1%)60 (0.0%)0 (0.0%)
      08Spelman T.47673 (15.3%)-19 (4.0%)8 (1.7%)81 (12.5%)0 (0.0%)
      09

      Drulovic J.180 (0.0%)5 (27.8%)0 (0.0%)0 (0.0%)110 (0.0%)0 (0.0%)
      10Fragoso Y. D.7315 (20.5%)20 (27.4%)6 (8.2%)2 (2.7%)1
      Case reports excluded from the meta-analysis
      0 (0.0%)0 (0.0%)
      11Bsteh G.12612 (9.5%)--4 (3.2%)2
      Case reports excluded from the meta-analysis
      0 (0.0%)0 (0.0%)
      12Perez A. C.843340 (40.3%)-87 (10.3%)56 (6.6%)1
      Case reports excluded from the meta-analysis
      0 (0.0%)0 (0.0%)
      13Yavorskaya V.302 (6.7%)--0 (0.0%)302 (6.7%)0 (0.0%)
      POOLED ESTIMATE
      Proportion [95% IC]14.98 [10.47 – 20.97]8.40 [2.90 – 21.92]4.44 [2.76 – 7.06]2.66 [1.79 – 3.92]9.36 [4.73 – 17.69]0.00 [0.00 – 1.17]
      I^2 [95% IC]95.48 [89–23 – 98.70]97.50 [91.71 – 99.64]88.61 [62.82 – 96.45]71.23 [30.81 – 90.50]0.00 [0.00 – 72.22]0.00
      ^ Case reports excluded from the meta-analysis

      4. Discussion

      The hospitalization rate of the overall MS population, as reported in the studies included in this analysis, was between 0% and 40% and the death rate was between 0% and 7%. Actually, the range mentioned above would include much closer values (respectively 0% - 21% and 0% - 4%) if the incidence reported from Perez et al. is not considered (hospitalization rate 340/843, 40%; death rate 56/843, 7%). In this study, that is a data collection using an administrative claims-based method (
      • Pérez C.A.
      • Zhang G.-Q.
      • Li X.
      • Huang Y.
      • Lincoln J.A.
      • Samudralwar R.D.
      • Gupta R.K.
      • Lindsey J.W.
      COVID-19 severity and outcome in multiple sclerosis: results of a national, registry-based, matched cohort study.
      ) several limitations were reported, including the risk of possible misclassification, underreporting and/or inconsistent ICD coding practices being.
      The pooled estimate of the hospitalization rate was 14.98% (high heterogeneity: 95.4%), lower than the rate reported in the systematic review on COVID-19 in pwMS from
      • Barzegar M.
      • Mirmosayyeb O.
      • Gajarzadeh M.
      • Afshari-Safavi A.
      • Nehzat N.
      • Vaheb S.
      • Shaygannejad V.
      • Maghzi A.-H.
      COVID-19 among patients with multiple sclerosis: a systematic review.
      (20.7%). The collection of data from different countries, often referred to different periods of pandemic and based on different study designs, could explain these results. However, the hospitalization rate of the general population is ranging from 2.9 to 30% of all COVID-19 cases (

      Coronavirus Disease 2019 (COVID-19): Epidemiology update. Updated: September 20, 2020. Accessed September 21, 2020. health-infobase.canada.ca/COVID-19/epidemiological-summary-COVID-19-cases.htm.

      ) and that of pwMS falls in this interval. The demographic characteristics of pwMS are generally younger with more females than the general population, which should automatically put this cohort of patients at lower risks of hospitalization (
      • Barzegar M.
      • Mirmosayyeb O.
      • Gajarzadeh M.
      • Afshari-Safavi A.
      • Nehzat N.
      • Vaheb S.
      • Shaygannejad V.
      • Maghzi A.-H.
      COVID-19 among patients with multiple sclerosis: a systematic review.
      ).
      In this analysis only 157 out of 5138 (3.1%) patients presented a fatal event, resulting in a pooled estimate of 2.66 (95%CI: 1.79-3.92), with a high heterogeneity among studies (I2= 71.2%), that is a number in line with previous studies (
      • Barzegar M.
      • Mirmosayyeb O.
      • Gajarzadeh M.
      • Afshari-Safavi A.
      • Nehzat N.
      • Vaheb S.
      • Shaygannejad V.
      • Maghzi A.-H.
      COVID-19 among patients with multiple sclerosis: a systematic review.
      ). No deaths (out of 107 subjects) were observed in the group of patients treated with cladribine and even if the size of this group is small, this observation indicates that there is no evidence of an increased risk of severe COVID-19 in pwMS receiving cladribine.

      Declaration of Competing Interest

      This scientific collaborative research project research thesis has been funded by Merck Serono S.p.A., Rome, Italy, an affiliate of Merck KGaA (CrossRef Funder ID: 10.13039/100009945). AA is an employee of Merck Serono S.p.A., Rome, Italy, an affiliate of Merck KGaA, Darmstadt, Germany.

      Acknowledgments

      We really thank authors which have provided some additional data of their samples or have confirmed some unclear measures.

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